For the production of low density nuclear fuel pellets of uranium dioxide, plutonium dioxide or mixtures of uranium dioxide and plutonium dioxide two basic methods of achieving low densities are feasible. The first entails the production of an oxide containing the correct amount of potential energy such that the desired density is achieved after sintering at the chosen time and temperature profile in the sintering furnace. The second method entails the production of a standard quality of dioxide powder which sinters to a higher density than that required and the incorporation in pellets of the dioxide powder of the requisite amount of a removable additive which will induce the correct amount of porosity within the pellets after sintering.